1. Field of the Invention
The present invention relates to a valve and a production method thereof.
2. Description of the Related Art
Since 1980, there have been disclosed various valves produced by a microprocessing technology (hereinafter, referred to as “microprocessed valve”) (see, for example, K. W. Oh and C. H. Ahn., “A review of microvalves”, J. Micromech. Microeng. 16, R13-R39, 2006)
According to the disclosures thereof, the microprocessed valves are classified mainly into two categories of passive valves and active valves.
On the other hand, as another microprocessed valve, there is known a microprocessed valve including, for example, a one-shot valve designed to operate only once.
As the application of the one-shot valve, it is effective to use the one-shot valve as a valve for triggering a mixing reaction in a lab-on-a-chip or as a valve for delivering a medicine sample to a smart micro pill.
In a case where the one-shot valve of those applications is structured as a temperature actuated valve which is operated depending on temperature, the one-shot valve can be used for pressure release of a fuel cell for use in, for example, a small portable device, having a small fuel tank.
That is, the one-shot valve can be applied to a rupture system for releasing a pressure when a pressure in a fuel tank is abnormally high due to temperature rise.
The term “microprocessed one-shot valve” herein employed refers to an operation valve which is designed to operate only once and produced by a microprocessing technology as described above.
Hitherto, there has been disclosed a microprocessed one-shot valve which operates depending on temperature and pressure (see A. Debray, M. Shibata, and H. Fujita, “one-shot micro-valve with temperature dependent operation”, In Proceeding of the Power MEMS 2006 Conference, pp. 137-140, 2006).
This document discloses a microprocessed one-shot valve having a structure in which an upper end of a channel bored in a silicon wafer is blocked by an underlayer formed by stacking chromium and copper and a low melting point alloy coating an upper portion thereof.
When the temperature of the microprocessed one-shot valve is higher than the melting point of the alloy and the pressure difference between the inside and the outside of the channel is high enough to break the chromium/copper layer, the valve is in an open state. In this case, the pressure difference is normally set to 100 kPa or more.
A reason for this setting is to reduce a risk of breakage of the underlayer during a production process, because when the underlayer is designed to be broken at a pressure difference of less than 100 kPa, strength of the underlayer becomes lower.
Accordingly, this structure is suitable in designing a valve which opens at a pressure difference of 100 kPa or more.
Further, thermal expansion ratios of chromium and copper which constitute the underlayer are different from each other. Accordingly, the breakage strength of the underlayer depends on a temperature in some cases.
Therefore, in order to realize the underlayer which is opened at a predetermined temperature or a predetermined pressure difference, caution is required.
On the other hand, O. Guerin, L. J. O. Dubochet, J. -F. Zeberli, Ph. Clot, and Ph. Renaud, “Miniature one-shot valve”, In IEEE MEMS Conference, pp. 425-428, 1998 discloses another microprocessed one-shot valve.
According to the microprocessed one-shot valve as disclosed in this document, a closed micro channel is opened by melting of a polyethylene layer.
Accordingly, the temperature at which the microprocessed one-shot valve is operated can be set depending on the melting temperature of polyethylene.
Further, P. Griss, Andersson H., and G. Stemme, “Expandable microspheres for the handling of liquids”, Lab Chip, 2, pp. 117-120, 2002 discloses still another microprocessed one-shot valve formed with microspheres.
In the microprocessed one-shot valve as disclosed in this document, the volume of the expandable microspheres increases about 60 times larger at a set temperature or more.
The microspheres inserted into the channel close the channel when expanded.
The microprocessed one-shot valve is structured so as to be capable of switching from an open position to a closed position.
Further, J. T. Santini, A. C. Richards, R. Scheidt, M. J. Cima, and R. Langer, “Microchips as controlled drug-delivery devices”, Angew. Chem. Int. Ed. 39, pp. 2396-2407, 2000 discloses still another microprocessed one-shot valve triggered by a current.
The microprocessed one-shot valve is disposed in a cistern mounted to an inner portion of a silicon wafer.
To an upper portion of the cistern, a metal layer serving as an anode is deposited. Another metal layer serving as a cathode is deposited to a side of the cistern.
By putting the microprocessed one-shot valve into an electrolyte and imparting a potential difference between the anode and the cathode, the anode is oxidized. After that, the anode metal layer is dissolved in the electrolyte. With this mechanism, switching from the closed position to the open position is performed.
Further, U.S. Pat. No. 4,313,453 discloses a thermally operated valve.
The thermally operated valve is a member sealed by a solder to an inner portion of a connection portion at which two metal pipings are connected to each other, and stops flow in the metal pipings. By applying heat to the solder, the solder is melted, the thermally operated valve is opened, and flow in the metal pipings is enabled.
Further, U.S. Pat. No. 5,526,385 discloses a safety device used for protection against abnormal overpressure of a nuclear reactor pressure vessel.
The safety device has a structure in which a pressure compensation opening is sealed by a solder. During a normal operation, the solder has a solid form and the pressure compensation opening is closed. At a higher temperature, the solder is melted.
Further, by overpressure in a pipe, a melting solder is pushed to open the pressure compensation opening of the pipe.
The inventions according to the above-mentioned conventional examples have several problems as described below.
For example, when a temperature sensitive microprocessed one-shot valve is used, it is desirable that the operation temperature of the temperature sensitive microprocessed one-shot valve can be set variously depending on an intended purpose.
However, in the case of the microprocessed valve as disclosed in A. Debray, M. Shibata, and H. Fujita, “one-shot micro-valve with temperature dependent operation”, In Proceeding of the Power MEMS 2006 Conference, pp. 137-140, 2006, the production of the microprocessed valve which opens at a pressure difference smaller than 100 kPa becomes difficult in some cases. Further, depending on the material structure of the underlayer, there may be a case where a design providing an accurate opening pressure difference becomes difficult.
Further, in the case of the microprocessed valve as disclosed in O. Guerin, L. J. O. Dubochet, J. -F. Zeberli, Ph. Clot, and Ph. Renaud, “Miniature one-shot valve”, In IEEE MEMS Conference, pp. 425-428, 1998, desirable operation temperature cannot be set depending on an intended purpose.
On the other hand, in order to use the microprocessed valve for releasing a pressure, switching from the closed position to the open position is necessary.
On the contrary, in the case of the microprocessed valve as disclosed in P. Griss, Andersson H., and G. Stemme, “Expandable microspheres for the handling of liquids”, Lab Chip, 2, pp. 117-120, 2002, in the operation of the microprocessed valve, switching only from the open position to the closed position is possible.
Further, in order to use the microprocessed valve as a pressure release mechanism or various liquid-feeding initiation mechanisms for a fuel tank, it is required that the microprocessed valve can operate in an arbitrary use environment.
On the contrary, in the case of the microprocessed valve as disclosed in J. T. Santini, A. C. Richards, R. Scheidt, M. J. Cima, and R. Langer, “Microchips as controlled drug-delivery devices”, Angew. Chem. Int. Ed. 39, pp. 2396-2407, 2000, the operation of the valve is limited by an electrolyte environment.
Further, the microprocessed one-shot valve has the following characteristic points in addition to a point that the microprocessed one-shot valve is used while being incorporated in a small system.
One characteristic point is that the microprocessed one-shot valve has high sensitivity to an ambient temperature because it is small.
The microprocessed one-shot valve has this high sensitivity because thermodiffusion has a faster influence on the valve of a smaller size.
Another characteristic point is that, because a microprocessing technique, in particular, a MEMS technique can be used for the production method, batch production for producing multiple devices at the same time on the same support body is enabled.
This enables reduction in production costs and manufacture of a control mechanism such as a heater at the same time and directly in the vicinity of the microprocessed one-shot valve.
However, in examples using a solder as disclosed in U.S. Pat. Nos. 4,313,453 and 5,526,385, the production has to be achieved by a typical macro technique.
Accordingly, the size of the device cannot be reduced to 2 to 3 mm3 or smaller. Further, the production cannot employ the batch processing.
In addition, the control mechanism such as a heater cannot be directly incorporated.
The problems to be solved in the temperature sensitive microprocessed one-shot valves described above can be summed up as follows.
When an ambient temperature is higher than a predetermined temperature Tc and when a pressure is higher than a predetermined pressure Pc, a pressurized fluid (gas or liquid) needs to be ejected.
That is, the valve has to be structured such that, at a temperature equal to or lower than the predetermined temperature, the valve connected to a tank accommodating a pressurized gas or liquid is kept closed, and at a temperature equal to or higher than the predetermined temperature, the valve is opened.
In this case, it is desirable that the opening temperature of the valve can be set to an arbitrary temperature, and the valve can be used in both a liquid environment and a gas environment.
Further, the valve has a small size which is typically smaller than a size of 2 to 3 mm3.
Further, the production method therefor is of a batch mode. In order to trigger the opening on demand, it is necessary that a heater be easily incorporated into the system.
Further, at the time of opening the valve, when there exist contents other than a fluid to be released, for example, solid substances or solid particles, it is desirable that scattering thereof can be prevented. In this case, the channel itself can function as a filter.